1. Field of the Invention
The present invention relates to a method and apparatus for quality control of molded articles manufactured by means of injection molding machines o die casting machines.
Specifically, the present invention relates to a method which includes weighing individual molded articles after they have been ejected from the mold. The actual weight of the molded articles is compared to a desired weight and the resulting difference signal is used for influencing the injection molding machine or the die casting machine and/or the injection mold in order to correct the weight of the molded articles.
The present invention further relates to an apparatus for carrying out this method which includes an electronic test balance arranged after a discharge hopper for the molded articles of the injection molding machine or die casting machine. The electronic test balance is used for providing an output signal for influencing the injection molding machine or die casting machine and/or the injection mold.
2. Description of the Related Art
In known quality control systems of the above-described type, so-called discharge test balances are used which usually operate with a range of accuracy of .+-.0.1 g and which are constructed in such a way that only a time period of less than 1 second is required for each individual weighing procedure. Within this short period of time, the output signal of the discharge test balance can be utilized for influencing the control of the injection molding machine or die casting machine and/or the injection molding tool of the machine, in order to effect a further optimizing of the quality of the subsequently manufactured molded articles.
The known quality control systems of the above-described type can be used in a manufacturing plant in connection with an operating injection molding machine as long as a range of accuracy of .+-.0.1 g is sufficient for the quality determination of the molded articles.
However, in many cases, the molded articles must meet quality requirements in which a range of accuracy of the above-mentioned order of magnitude is entirely insufficient. This is because in certain situations it may be that ranges of accuracy are required which are between .+-.0.01 g and .+-.0.001 g.
In such cases, in accordance with the known prior art, an exact weighing of the individual molded articles under laboratory conditions is required. Thus, the quality control was substantially time-consuming and expensive.
It is, therefore, the primary object of the present invention to provide a quality control system of the abovedescribed type which can be used in a manufacturing plant in connection with operating injection molding machines or die casting machines and which can be utilized optionally either in the manner of a discharge test balance or in the manner of a laboratory balance.